Dry and Liquid Polymers

Organizations widely use water-soluble polymers in wastewater treatment to remove suspended solids and/or contaminants from the water. Unbeknownst to many consumers, municipal, industrial, and stormwater treatment systems regularly use these important substances.

In many cases, polymer solutions rapidly settle solids out of the liquid with properly prepared, activated, and applied polymers. With polymers, organizations can achieve liquid/solid separation in minutes or seconds. In contrast, if the process relied on gravity alone, the separation could take days or even months.

Many individuals are unaware of how polymers can help clarify and improve settling and dewatering operations—saving time, money, and energy.

What Are Polymers?

Polymers are a chain of molecules made up of smaller molecules called monomers. Monomers come together to form a chain, and the chain of monomers is called a polymer. There can be millions of monomer molecules in one polymer, and the more monomers there are, the longer the polymer chain.

Different monomers will create either anionic or cationic polymers. Both polymer types settle liquid-suspended solids, but they’re used in different applications.

Belt Press

Different Types of Polymers

Anionic polymers have a negative charge. Organizations commonly use this type of polymer in applications with inorganic solids such as clays and silts. We expect to see anionic polymers used for industrial applications such as:

  • Sand and gravel production
  • Drilling
  • Mining
  • Other mineral-based liquid-solid separation

Cationic polymers have a positive charge. Organizations often use this type of polymer to settle organic solids such as animal waste or vegetation. Customers use cationic polymers in processes such as:

  • Dredging
  • Municipal wastewater treatment plants
  • Food processing
  • Agricultural and dairy applications

Dry vs. Liquid Polymer

Wastewater treatment polymers usually come in either a dry granular form or a liquid, emulsion form.

Emulsion polymers are much easier to feed, dissolve into a water solution, and activate. The shelf life of an emulsion polymer is around 6 months.

Dry polymers require expensive equipment and a difficult process to dissolve and activate. When stored properly, the shelf life of dry polymers is infinite.

Dry and liquid polymers have different concentrations that determine their efficiency and benefits to an operation. Dry polymers generally have 95% or higher active chemistry vs. 30% – 40% active chemistry in emulsion polymers. While dry polymers are more expensive, customers can feed these polymers at a rate that is 2.5 – 3.0 times less than emulsion polymers.

When deciding between the two types for a waste treatment process, customers should consider:

  • Capital cost
  • Operating cost
  • Ease of operation
  • Shelf life
  • Performance

Your Northstar field technician will run bench-scale jar tests to compare emulsion vs. dry polymers, as well as different types of each one, to find the best product to achieve your operational goals.

Polymers in Wastewater Treatment

Polymers separate solids from liquids through a process called flocculation. Due to the name of the process, you will hear these specific water-soluble polymers referenced as flocculants or polymer flocculants.

The polymers’ ability to flocculate solids is central to their role in water treatment. They can be effective on their own and very impactful when combined with a coagulant.

Most industrial process water or wastewater includes sediment and particles with a negative electric charge.

The negative charge around each particle keeps them from coming together, creating colloidal dispersion. Negatively charged particles will not come together and can float in liquid suspension for hours, weeks, and even years. A simple example is the muddy water created by aggregate producers who wash sand and gravel.

A coagulant added to muddy water creates a coagulation process that neutralizes the particles’ negative charge. Once neutralized, the particles can come together to form larger particles called micro-flocs or pin flocs.

Coagulation charge neutralization process


Industry experts call the next chemical reaction flocculation, which helps create even larger flocs or macro-flocs.

In this step, a water-soluble polymer, or flocculant, helps bring together the coagulated particles to form longer and larger particle chains.

As the flocculant chains become larger, they become heavier and even visible to the naked eye. The flocculants create a larger particle with a higher mass-to-drag ratio, speeding up the natural process of sedimentation.

Flocculation charge site agglomeration process

As the settling process continues, a sludge forms at the bottom of whatever is holding the wastewater. As part of the wastewater treatment process, this sludge accumulates in:

  • Settling ponds
  • Sludge ponds
  • Clarifiers
  • Thickeners

Once the sludge forms, companies, and municipalities can manage and dispose of it through different methods.

Organizations do not use coagulants and flocculants to make sediment fall out of liquid suspension. Due to their ability to neutralize and agglomerate colloids, the chemicals also support dissolved air flotation (DAF) applications. In DAF applications, microbubbles pull the solids to the top of a tank, where a skimmer removes them.

Northstar’s Polymer Services

Whatever the application, a Northstar representative can help you find the best chemistry to achieve your performance goals at the lowest overall cost with the lowest amount of operator interface required.

Polymers play an important role in wastewater treatment. Besides separating solids from liquids, they also help thicken sludge and dewater contaminated material for easier handling and disposal.

Removing the water content from a waste sludge can change the waste properties from liquid to solid waste. This change has significant impacts on the disposal cost or tipping fee.

The Industry Standard for Solid vs Liquid Waste

The industry standard determining whether the waste is solid or liquid is EPA Method 9095B or “the paint filter test.” In this procedure, the tester places a sample of the waste sludge in a standard 60-mesh conical paint filter for 5 minutes.

If no liquid passes through the filter, the tester deems the waste solid and the organization can dispose of it more cost-effectively than liquid waste. In the industry, we would consider sludge passing the paint filter test to be dewatered.

Polymer flocculants expedite the dewatering processing by allowing water to leave the flocculated solids more freely.

Industries That Use Polymers to Treat Wastewater

Almost any industry that needs to remove solids from their wastewater stream can use polymers in their treatment process.

Aggregate producers use water to wash the sand, gravel, or other aggregates they produce. The wash water picks up dirt, clay, and silt during the washing process. To reuse or safely discharge this wash water, organizations must separate the solids from the water.

Many aggregate producers use settling ponds to hold the wastewater and allow sedimentation. As we noted, it can take a long time for sediment to fall out of liquid suspension.

Aggregate producers must stop production while cleaning their ponds and waiting for clean water. These shutdowns cause producers to lose production hours and increase labor hours.

However, polymers can increase the rate of sedimentation for aggregate producers. By using a polymer dosing system, producers can inject the polymer solution directly into their settling ponds.

The polymer dosing allows for easier management and disposal by:

  • Increasing the sedimentation rate
  • Providing clean water
  • Thickening the sludge at the pond’s bottom

Polymer Use in Wastewater Prep

Many operations also use polymers to prepare wastewater before the operation mechanically treats the wastewater in:

  • Clarifiers
  • Thickeners
  • Filter presses
  • Centrifuges
  • Other dewatering equipment

It’s important to note that not all wastewater treatment polymers are the same.

Northstar’s Custom Service for Wastewater Treatment

Northstar field technicians select specific chemistry for your unique process depending on your organization’s wastewater and operation needs.

Between the hundreds of different polymers available and the different make-down and feed systems for dry and emulsion polymers, it can be tough to know what is best for your application.

Your Northstar representative will provide the option(s) that best fit your needs and use jar testing to determine the best polymer chemistry. The right type of polymer will help you meet regulations, save money, and increase your operation’s success.

Northstar’s proprietary polymer controller helps you remove the need for constant operator adjustments while reducing your chemical costs and improving your system’s performance.

The polymers provided by Northstar Chemical meet the following certifications:

FDA, USDA, Kosher, Halal, non-GMO, GRAS, and NSF

For more information, visit our certifications & listings page.